1. Field of the Invention
The present invention relates to a rotary polygon mirror type light deflector for use in a light scanning device in a laser printer and, in more particular, to a fixing structure for fixing a polygon mirror with respect to a rotary member.
2. Related Art
A rotary polygon mirror type light deflector for use in a light scanning device in a laser printer, as disclosed in Japanese Patent Publication No. 6-165460 of Heisei, basically includes a rotary member (a rotor) rotatable due a magnetic force generated between a drive coil and a drive magnet, and a ring-shaped polygon mirror mounted on the periphery of the rotary member. For example, as shown in FIG. 5, a rotary member 203 is fixed to a rotary shaft 202 supported to a plate-shaped stator 200 through a bearing 201 for a bearing holder, and a polygon mirror 204 is mounted on the periphery of the rotary member 203. The polygon mirror 204 is pressed against and fixed onto the rotary member 203 only by a plate-shaped mirror holder 205 mounted on the rotary member 203 from the thrust direction. On the upper surface side of the plate-shaped stator 200 and on the lower surface side of the rotary member 203, there are provided a drive coil 206 and a rotor magnet 207 respectively, while the polygon mirror 204 can be rotated integrally with the rotary member 203 due to a magnetic force generated between the drive coil 206 and rotor magnet 207.
However, like such fixing structure for fixing the polygon mirror 20 as shown in FIG. 5, in a fixing structure of a type that the polygon mirror 204 is mounted on the periphery of the rotary member 203, there is required a mounting clearance between the rotary member 203 and polygon mirror 204. In the conventional fixing structure, because the polygon mirror 204 is simply pressed against and fixed onto the rotary member 203 from the thrust direction by the mirror holder 205, the polygon mirror 204 is easy to be displaced in the radial direction on the rotary member 203. That is, in the conventional rotary polygon mirror type light deflector, when the polygon mirror 204 rotates at high speeds or when a strong shock is given to the rotary polygon mirror type light deflector, then there is a possibility that the polygon mirror 204 can be displaced in the radial direction on the rotary member 203 by an amount corresponding to the above-mentioned clearance. In particular, if such displacement of the polygon mirror 204 occurs, then there is a possibility that the whole of the rotary member including the rotary member 203 and polygon mirror 204 can lose its balance, with the result that the rotation of the polygon mirror 204 is caused to vary, one or more of the surfaces of the polygon mirror 204 can be inclined, and vibration noises can be generated. Further, undesirably, due to transmission of the vibration noises to the whole of the light scanning device, the printing performance of a printer can be lowered, the performance of the bearing 201 can be worsened, and the bearing 201 can be burned up.